The Earthmovers—Centuries before Egypt's first pyramids were built, and long before Stonehenge, Native Americans constructed large earthen mounds in Louisiana.

Before the days of giant steel and stone monuments, people in North America made monuments of earth. They piled tons of it into oval, conical, and flat mounds for reasons that elude archeologists. Until now, the oldest mound complex was thought to be a 3,500-year-old site at Poverty Point, in northeast Louisiana. But a new study reveals that mounds at Watson Brake, just 55 miles away, are at least 1,900 years older than those at Poverty Point, making them the continent’s oldest known large-scale earthworks, and early evidence for organized society in North America.

Reca Bamburg Jones, an amateur archeologist, first recognized the importance of Watson Brake in 1981, after a timber company cleared the area. The largest mound, some 25 feet high, had been known to locals, including Jones. But after the clear-cutting, Jones noticed that it was connected by 3-foot-high ridges to ten other mounds that ranged in height from 3 to 15 feet, forming an oval enclosure 300 yards across. Jones and archeologist Joe Saunders of Northeast Louisiana University began an intensive study of the site in 1993. Last September they published their findings.

The people of Watson Brake, Jones and Saunders discovered, came there each year to hunt and fish along the Arkansas River, which in those days ran within half a mile of the site. They ate mainly fish like drum, catfish, and sucker. Layers of seasonal secretions in the fishes’ bones show that they were caught in the late spring to fall. Saunders also found remains of such animals as deer, turkey, squirrel, rabbit, turtle, and dog, as well as thousands of mussel and aquatic snail shells. None of the snail shells were broken, Saunders notes. So the people were somehow extracting the little buggers. We think they were steaming or boiling them. They were also eating wild plants, judging from the charred seeds of goosefoot, knotweed, and possibly marsh elder. These plants seed from summer to fall. Along with the evidence from the fish bones, this suggests that people visited the site only in the warmer months. Interestingly, these wild plants would later be among the first to be domesticated in eastern North America.

The Watson Brake people hadn’t invented pottery yet, although they did fire clay to make strange cubes and spheres—for what purpose no one knows. These small clay objects and tiny drills used for making beads were unlike anything at nearby Poverty Point, leading Saunders to believe Watson Brake could be older. Several dating techniques later showed that the Watson Brake mounds were built between 5,400 and 5,000 years ago. Nearly a thousand years before the pyramids were built and before the first pillars were erected at Stonehenge, Native Americans hauled around tons of gravel and soil, probably in skins and perhaps baskets, with a specific goal in mind. While the mounds on the northern half of the site follow the edge of a natural terrace, the southern mounds follow no natural feature. The southern half is purposefully completing the enclosure, the oval shape, says Saunders. That certainly shows planning. The two largest mounds show no signs of habitation, which suggests they were monuments of some kind.

Archeologists would expect a project on so large a scale to have been built by a settled people, with an elite group directing those of lower rank. Early Native Americans, who were probably nomadic hunter-gatherers, were not thought to have the social organization necessary for large-scale construction. Saunders thinks several small bands must have come together and cooperated over centuries to build and maintain Watson Brake. Other mounds in Louisiana, though not as firmly dated, seem to be from roughly the same period. For now, I think we can say it’s the earliest large-scale earthworks, says Saunders. Will it be predated? I have no doubt. And I don’t care. I think we’re going to find many more surprises that will make us reevaluate what was going on in that period of history.